Separation of plutonyl ions



Robert E. Connick complex acetate.

Q from a solution obtained .trat'ed by the use of carrier precipitate techniques.

2,843,453 SEPARATION 6F PLUTONYL IONS.

and William H. McVey, Berkeley, Calif assignors to the United States of America as represented by the United States Atomic Energy Com- 'mISSIOII'. 7 7

No Drawing. Application April 18, 1947 Serial No. 742,450

3 Claims. c1. 23-145 same in plutonium separation processes.

A great deal of'work has been carried out in solving the problem of separating plutonium from uranium and I radioactive fission products which are constituents of the I uranium mass upon its removal from a neutronic reactor. Various methods of separation have included those based on adsorption, electrodeposition, and distillation of plutonium from the mass. However, the most successful methods at present are based upon oxidation-reduction reactions of plutonium and precipitation of plutonium compounds. It has been found that plutonium has at least two states of oxidation. In lower states of oxidation, plutonium has a valence of +3 and +4 and is substantially insoluble in water as a phosphate or fluoride. In its higher state of oxidation plutonium is water soluble as a phosphate or fluoride but forms In the higher state of oxidation plutonium has a valence of +6 and this, oxidized plutonium isv capable of forming a plutonyl ion having a probable structure PuO It has been'found that by .the use of I suitable oxidizing and reducing agents the oxidation state of plutonium may be changed without aifecting the oxidation state of uranium. Thus, by converting the plutonium to the Pu+ state without changing the uranium from its +6 oxidation state, plutonium may be precipitated as the phosphate or fluoride from a solution containing plutonium, uranium and fission products, leaving uranium in solution together with most of the fission products. Several of the fission products, however, are insoluble as phosphates especially Zr and Cb, andthese will precipitate with plutonium in the +4'state. 'These combined plutonium and fission products phosphates an insoluble are then dissolved in an acid solution, and the-plutonium is oxidized to the +6 valence state. The plutonium may then be separated from these fission products either lay-precipitating the plutonium as the sodium; plutonyl acetate, or the fission products maybe precipitated from -the solution as the phosphates or fluorides, leaving 'the Pu in solution. v e V Because of the very minute quantities of plutonium usually contained in the mass obtained froma neutronic reactor it is not feasible to precipitate plutonium directly by'dissolving this mass with a suitable inorganic acid. Plutonium'may, however be separated from uranium, decontaminated and concen- It has been found that certain precipitates called carriers will carry plutonium ions from solution; thus, bismuth phosphate has been found to carry theiPu+ ion and sodium uranyl acetate has been found to carry the Pu ion; There are also numerous other precipitates which will carry plutoniumbut the two above-mentioned have been found to be especially satisfactory carriers. By the use of these carriers andalternate oxidationareduction cycles plutonium may be concentrated suflicientl y so that it may be precipitated directly from solution.

In the oxidation-reduction method of separation of plutonium, a process used is the bismuth phosphate: sodium uranyl acetate process. nium mass is removed from the neutronic reactor; dissolved in nitric acid to uranyl nitrate, plutonium in radioactive fission products.

from carrying with sion'products which form insoluble phosphates.

+6 state. A second bismuth phosphate precipitate is then formed and separated from with it phosphate insoluble fission products and leaving This oxidation-reduction cycle 1 solution is obtained substantially Pu+ ions in solution. may be repeated, until a free of fission products. The solution, however, usually contains plutonium in such dilute concentrations that it" before it may be separated is necessary to concentrate it from the solution by direct precipitation. This may be accomplished by oxidizing the plutonium to the +6 state and forming a carrier precipitate of sodium uranyl aceacid after which the plutonium the Pu+ ion in solution.

It is often desirable to convert-the. Pu+f ionto,v the Pu' ion. This is usually accomplished by theoxidation of the Pu+ ion with a suitable oxidizing'agent such as Cr O or BiO aocordingto the following reactions."-

In order to obtain plutonyl ions free of excess 'oxidizing agents and reduction products it is customary to ,pfre-"f the sodium plutonyl. acetate This precipitate is thendissolved in an incipitate the plutonyl ion as NaPuO AC organic acid to obtain a solution containing the plutonyl ions. It is often desirable, however, to obtain a plutonyl ion solution free from the acetate ion and this "object may be accomplished advantageously by employing the-- plutonates, and suitable methods for preparing such plutoe nates.

The alkaline earth plutonate's, which are the subject of 1' i this invention, are-comprised of compounds consisting of an atom or atoms of, an alkaline earth metaLfheXavalent plutonium, and Joxygencombined with or free of Water of crystallization. These compounds maybe precipitated from an acidic solution containing the plutonyl ions, by the addition of a soluble 'salt of an alkaline earth metal, .such .as. the nitrate or chloride, and the conversion of the acid solution to analkaline statejby" suitable means, such to an alkaline state, may be by the addition ofthe metal, such as Ba(OI-I) Ca(OH) or the'like.

alkaline earth groups, and water of crystallization,

ratios are generally non-integral.

the polyplutonate (MO),,-(PuQ )m, wherein I represents Patented. July 15,1958 1.

In this process the uraj and give a solution containingthe +4 state and ions of? A bismuth phosphate pre- 1 cipitate is formed in this solution and separated there-1 it plutonium and certain of the fis- The bismuth phosphate precipitate is dissolved in nitric or other suitable acid, and'the plutonium is oxidized to its the solution carrying 7 of this invention to provide a simplified method of converting plutonous ions to plutoas' the addition of NI I OI-I or pre'ferably NaOH. The addition of a soluble alkaline earth" compound, and conversion o f the solution from acid carried out simultaneously; hydroxide of the alkalinejeart 0 an alkaline earth metal, and a and m are small whole numbers.

The barium plutonates range in color from light brown to dark red-brown. Extensive solubility determinations have'been made with the barium, magnesium and calcium plutonates, and although the solubilities varied somewhat with the methods of preparation and the length of time for which they were maintained in the solution, it was found that these plutonates were generally quite insoluble, with barium plutonate prepared with NaOH being particularly insoluble and under optimum conditions having a solubility as small or smaller than that of barium sulfate.

The solubility and stability of the plutonates are someto the method of converting the plutonyl solution from acidic to basic. Thus, where the plutonates are precipitated in a solution made basic with NH OH, the solubilities are somewhat higher than for The plutonates prepared with NH OH also tended to dissolve somewhat under washing, in contrast to the plutonates prepared by the use of NaOH which were stable under washing. It is, therefore, generally preferable to use NaOH rat er than NI-L OH in the preparation of the plutonates. There may, however, be special cases where the NH OI-l is preferable, such as where the plutonyl solution is prepared by the oxidation of Pd with the argentic ion. The solubility of the plutonates also varies somewhat with the time interval during which they are in equilibration with the precipitating medium and it is generally desirable to permit the precipitate to in very small concentrations. This is particularly true of the barium plutonates which have exhibited solubilities as low as 0.00171 gm. Pu/l.

The formation of the plutonates may be illustrated by the following examples.

EXAMPLE I A solution of plutonium in nitric acid solution was oxidized to Pu+ by BrO Ba(NO was then added to the solution to furnish the barium ion and an excess of NaOH was introduced into the solution. A reddish brown precipitate of barium plutonate was formed.

EXAMPLE II Pu+ contained in a nitric acid solution was titrated with Ba(OH) to an acidity value of pH 11.3 and the solution was then heated to 90 C. for two hours and solubility of the barlum plutonate, which was a reddishbrown precipitate, was 0.15 g./l.

EXAMPLE III only 12 mg. Pu/l.

The following tables will illustrate the solubility of the 731'10115 alkali metal plutonates. The method of preparaion is indicated in the heading of the tables.

4 Table I.-S0lubility of barium platonate in NaOH [B1(NO3)2 0.1 lVI, P11(VI) ca. 0.46 g./l.,' NaOH 1 JNI] Time of Sampling Solubility (mg. Full.)

0 a 141 15 min 142 30 min 129 1 hr 77. 3 1 hrs 64. 9 2% his 54.6 3% hrs 22. 7

19 hrs Table II.-S0lubility of magnesium platonate in ammonia [h IgOlOah 0.1 hi; P11(VI) 0.46 g./l.,' 0ft. 6 RI NHiOH] Solubility (Lug. Pu/l.)

Time of Sampling Table lH.--SOZability of calcium plutonale in ammonia [uOa(N0a)z 0.1 M; Pu(VI) 0.46 g./l.; ca. 5 M NH4OHE] Time of Sampling Solubility (mg. Pu/l.)

10 min 338 31.3 200 332 316 42% hrs n, W

Another aspect of this invention has to do with procedures for the recovery of plutonium from solutions containing plutonium in the +6 oxidation state. recovery of plutonium from neutron irradiated uranium by the sodium uranyl-acetate decontamination and concentration procedures previously described, a solution compound with a very low solubility. The new compositions of matter which are the subject of this invention are particularly suited for this purpose and the separation maybe made by the following method. A sol-= 5 What is claimed is: References Cited in the file of this patent 1. A process otseparating plutonyl ions from acetic Friend: Textbook of Inorganic Chemistry, vol. 7, part acid amons contamed m an aqueous acldlc SOI U 3, page 308 (1926); 1111131. by C a l fl fl & comprising adding a soluble barium mineral acid salt to London said SOIHUODI, alkalizmg said solution whereby a plu- 5 Deming; Gweral Chemistry, 3rd ed page 4 (1930); tomum-contammg preclpltate forms, and separatlng said pubL by John Wiley & Sons, New York, 1

Pffi p from the acetic-acid-aniofls'containing S0111 Villar: Journal of Chemical Education, vol. 19, pp.

tlon. 329-330 (1942).

2. The process of claun 1 wherein the solutlon 1s alkas chemiwl a Engineering News 1 23 lizedby the addition of sodium hydroxide while the solu- 10 No 23, 21904193 (1945) mm 18 at elevated p a a Connick et al.: MDDC335, 3 pages, July 2, 1946.

I The P Q 9 clafm wherem i Solution wlth Seaborg et al.: The Transuranium Elements, part I, the formed'preclpltate is allowed to dlgest for several 530 549 02. 07 330 1949 1 w. hours prior to separating the precipitate. 1 1 Book Co Inc, New Y0rkN Y, V 

1. A PROCESS OF SEPARATING PLUTONYL IONS FROM ACETIC ACID ANIONS CONTAINED IN AN AQUEOUS ACIDIC SOLUTION, COMPRISING ADDING A SOLUBLE BARIUM MINERAL ACID SALT TO SAID SOLUTION, ALKALIZING SAID SOLUTION WHEREBY A PLUTONIUM-CONTAINING PRECIPITATE FORMS, AND SEPARATING SAID PRECIPITATE FROM THE ACETIC-ACID-ANIONS-CONTAINING SOLUTION. 